Signaling-circuit.



W. H. MARTIN.

SIGNALING CIRCUIT.

APPLICATION FILED AUG-27, I917 1,254, 146. Patented Jan. 22, 191&

I I INVENTORL [29:4 WH/Mariz'n' BY @W A TTORNEYS.

" UNITED STA'fiEfi: PATENT OFFICE,

WILLIAM H. MARTIN, OF NEW YOBk, N. Y., ASSIGNOR '10 AMERICAN TELEPHONE AND TELEGRAPH COMPAKY, A CORPORATION OF NEW YORK.

' Mahatma-amour.

To' all whom it may concern Be it known that 1, WILLIAM H. MARTIN residing at New York city, in the county oi Bronx and State of New York, have invented certain Improvements .in Signaling-Circuits, of which the following is a specification.

This invention relates to circuit arrangements for signaling systems wherein signals may be either transmitted from or received at the same station. In its more specific aspects this invention is embodiedin a subscribers telephone station, hereinafter termed, in accordance with common usage, a

substation, and more particularly in the combination of a substation and a telephone line. Its object is to provide a signaling circuit arrangement which in cooperative coinbination'with a similar and equal communicating arrangement or station shall deliver the maximum amount of energy to the received and transmitted energy. and further characterized b' the absence of side tone.

The object o the invention is attained, in its specific aspect, by providing a substation consisting of transmitter, receiver, auxiliary resistance,rand a transformer havin a plurality of windings which, in com ination withla tele hone line, shall 'satisfyihc following fun amental requirement: Given two identical substations designed for invariable; two-way communication, and connected by a line of given-impedance and length, .the

amount of energy absorbed by'the receiver at the receiving station shall be the maximum part of the total telephonic energy developed by the; transmitter atthe transmitting station consistent with invariable; two-way communication, and, as hereinafter explained, consistent was a desirable amount I of discrimination against disturbing line Specification of Letter: Intent.

noise. This fundamental requirement ina be stated in terms of the following SIIbOI'dk natere uirements which are necessary for its satis action: (1) The transmitter and receiver shall be conjugate, that istiiere shall be negligible side tone in the receiver in consequence of the actuation ofv the transmit- Patented Jan l22, 1918. 1

Application fled'AugustM, 191'3'. Serial No.188329.

ter by sound waves; (2) the line and auxiliaryresistance shall be conjugate in order that none of the energy absorbed -by the substat on from the line shall be wasted in said auxiliary resistance; (3) for a given line i having a definiteim edance the telephonic energy delivered by t e transmitter shall be a maximum; (4) the amount of energy delivered by the line to the substation shall be a maximum, in other words the impedance of the substation as seen from the line shall be equal to the im edance of the line; (5) at a small sacrifice o efliciency it shall be possible to discriminate eflectively against disturbing line noise as distinguished from the telephonic signals from the communicating station.

A substation satisfying the above-mentioned requirements isideal in that its overall efliciency from transmitter of one SllbStfir tion to receiver of the communicating substation is a theoretical maximum whichcannot be exceeded by any invariable substations whether satisfying the requirement of transmitterand receiver conjugacy or not.

It is further ideal in the sense that a minimum number 0? elements is employed since at least one auxiliary elementisnecess'ary to secure freedom from side tone. J.

It mi ht be inferred that the addition of.

an auxi iary resistance element, necessary as at the same time necessarily reduce the efli-, cien c of the substation since energy is ,unavol' abl efiiciency of 4the substation of my invention is atheoretical 'maximumwhich cannotbe exceeded by any two-way substation whether with or without side tone the following con- 'siderations.w11lshow. .T e. simplest form of substation for i variable .twoeway communif 1 it is to secure freedoxnfrom side tone, would '90 wasted in said auxiliary resist- 1 .ance. 'T at th s is not the'case and that the v station is wasted in the transmitter and fifty per cent. of the energy delivered by the transmitter is wasted in the receiver. Further such an arrangement labors under the disadvantage of full side tone. In the substation of my invention fifty per cent. of the energy delivered by the line to the substation is Wasted in the transmitter but none in the auxiliary resistance if said auxiliary resistance and said line are conjugate; hence the efliciency is as great as that of the simple series substation. When transmitting no energy is wasted in the receiver but fifty per cent. of the energy delivered by the transmitter is wasted in the auxiliary resistance.

. The transmitting efiiciency is therefore also a theoretical maximum and neither transmitting nor receiving efliciency is reduced by the addition of the auxiliary resistance which is necessary to secure freedom from side tone. The foregoing consideration will serve to explain the desirability of having the line and auxiliary resistance conjugate as well as the transmitter and receiver.

In my present invention I provide a sub station comprising transmitter, receiver, auxiliary resistance and transformer and so proportion said component elements and so relate them to a telephone line and to each other that, in combination with said telephone line, said substation. satisfies all of the foregoing requirements.

a I have discovered that the aboveanen "tinned requirements may be satisfied by 'a number of arrangements employing the minimum number of elements and all equally eflicient and without side tone.

' While theoretically all these arrangements are equally good, practical considerations 7 make certain arrangements preferable.

so I Fig. 4 is a' similar diagram indicating the caption. tion 0%,

My invention will now be fully understood by reference' to the accompanying drawing in which:

Figure 1 is a schematic diagram of one form of substation in accordance with this invention. Fig. 2 is a circuit diagram showing the arrangement of the substation in greater detail. 'Fig. 3 is a circuit diagram indicating the relative direction during transmission of current How" in the circuit shown in Fig. 2, the dotted lines indicating elements through which no current flows.

relative direction of current flow during re- In the above diagrams the direcr ding of the transformer coils and the direction of current flow as indicated are merely conventional and only hold true for particular values of the elements of the substation. It will be clear from an inspection of the design formulae hereinafter set forth that the winding ratio r may, in general, be either positive or negative, depending upon the values of the line and transmitter resistances. If, therefore, for any particular design the winding ratio results in a negative value, it is to be interpreted as meaning that the relative direction of winding of the coils whose winding ratio is negative must be the reverse of that shown in the dig'gram.

In order to illustrate the scope of my invention and elucidate the principles on which all specific embodiments rest, a general theoretical discussion will now be given which applies to all substations satisfying the requirements heretofore stated in this specification. In this discussion and the equations and formulae included in this specification the subscripts 1, 2, 3 and 4 will refer to transmitter, receiver, auxiliary resistance and line respectively. Thus 1,, 1,, I I will denote the currents flowing in transmitter, receiver, auxiliary resistance and line respectively, while'llwill denote the resistance of the transmitter, R, the resistance of the receiver, etc.

Consider a substation consisting of transmitt-er, receiver, auxiliary resistance and appropriate transformer windings, connected to a line of given impedance. In practice the .line connects two similar and equal substations between which communication is established. It is a well known principle that if a terminal impedance is connected to a source of electromotive force through a line of impedance where R, is the resistance and R, the react a'nce component of the impedance, the ter minal impedance must be R,-iR for maximum absorption of energy. In particular if the line impedance has no reactance component, the impedance of the terminal arrangement as seen from the line should be equal to the resistance component of the impedanceof the'line. The condition, then, that the substation shall have maximum en 'ergy absorption from the line is that its impedance, as seen from the line,shall be equal to the line impedance. The significance of the foregoing statement'may be explained by reference to Fig. 2, as follows:

Let the substation be disconnected from the line andlet the impedance of-thesubstation be measured across terminals (1 and d. I Then the impedance so measured shall be, equal to the impedance of the line. With the line terminated at each end by a' substation satisfying this condition, the line may be retransmitter, line and auxiliary resistance. 65

placed, as regards transmission from either substation, by an impedance element of re aistancc equal to the impedance of the line. Any reactance effect, which is in practice small, may be eliminated by neutralizing,-

reactance and, therefore, need not be considered The condition, than, that the substation have maximum energy absorption from the line is that its impedance asseen from the line he a pure resistance of value equal to the impedance of the line, This condition is evidently equivalent to the following requirementplet an electromotive force be nnpressed on the substatlon terminals through a resistance equal to the impedance of the line; then the energy consumed in the substation shall be equal to the energy consumed in said resistance.

Further, line and auxiliary resistance are conjugate by requirement (2}, as herein before stated, or in other words, the auxiliary resistance is connected to points of equal potential with respect to an electromotive force applied to the line terminals. Moreover, the impedance of the substations as seen from the line should be equal to that of the line, Let, then, an eieetromotive force ill, be impressed through a resistance R, on

a substation whose transmitter and receiver resistances are E, and respectively, and let the resultant currents in line, trans1nitter and receiver be L, I, and l irespectively. The impedance across the substation terurinals must be H, asseen from the line and the total resistance in series with E, is 2B,, and since the current in the line is 1,, it follows that 2R, The totai. energy consumed may then be ex pressed by the formula 9 E 2 Lil *i' 1534 1.221%? Since the energy consumed by the substation is equal to that consumed by the resistance R, and is therefore onehalf of the total energy consumed, it follows that requirement 4 may be formulated by the following:

Mar (ar (ar o), This equation states that the energy con sumption in the resistance R, is equal to that in substation, and that the substation is equivalent, as seen from the line, to a rv stance of value 1R4. M Similarly, if transmitter and receiver are conjugate the condition that the transmitter shall have its maximum. output to line and auxiliary resistance maybe formulated as follows: Let an electrom'otive'force E, iuthe transmitter produce currents 1,,1, and. 1, in

lhen, for maximum output, it follows that the impedance so measured is equal to the -1mpedance of the transmitter.

words, the impedance ofthe combination as seen from the transmitter is equal to that of the transmitter itself.

In other As hereinafter shown for "the particular embodiments of my invention, equation (2) follows as a consequence of the conditions oi" double conjugacy and equation (1). Therefore the foregoing fohr requirements impose but three restrictions on the substation.

To complete the general discussion it remains to consider the energy division bc-' tween receiver and transmitter when receiving, and'between line and auxiliary resistance when transmitting. Let W, be-thc total amount of telephonic energy developed by the transmitter at the transmitting substation; then, by equation (2), 1/2VV is the amount of energy delivered to line and auxiliary resistance. Let the amount of energy taken by the auxiliary resistance be o times that taken by the line, then the amount of energy taken by the line is "(1 +a:) so that the transmitting elficiency is measured by s 1 (1 +9?) (3) Of the total energy delivered to the receiving substation, let the transmitter absorb'g times that absorbed by receiver; then the receivingefiiciency is measured by a of the transmission efiicicncy and receiving efliciency; therefore the over-all efliciency is by formulae 3) and (4):

care) If a: study were independent, clearly the over-all efliciency would be a maximum for w::y:':0.. For all substations embodyingthe 1 principles of my invention it may be readily shown, however, that w and 3/ are connected by the relation avg =1. Eliminating a: from clot-trot loti've force by means of this relation, the over-all efficiency be the above formula the expression for comes In order to demonstrate the above statement. namely that try :1. designate the elements or branches T, 1%, X and L by 1, 2, 3 and 4, respectively. and let 1 and :2 be conjugate and also 3 and *t be conjugate. Furtber it will be assumed for an clcctromotivo t'orce in branch 4, equation (1) is satisfied while for an electrolnotive force in branch 1, equatimi (2) is satisfied. Let S denote the current. produced in branch or element 1 by a. unit clectromot'ivc force iubranch 1. S the current produced in branch 2 by a unit elect romotive force in branch 1, etc. Then by the conjugacy of branches 1 and 2 and branches 3 and +L, it follows that 12 34 Also by equation (1) 1 10 1 (S yli Now it is a fundamental principle which is deduoible from elementary al; 1'i *bra that 5 5:3 That is. the current set up inbranch 1 by a unit electromotive force in branch 4 isequaI to. the current setup in branch 4 by aunit electromotive force in branch 1. Multiplying equation (1') by'R and equation (2) by R and subtracting it follows that:

(an ne mut. to

Now in accordance with the notation adopted in this spccilicat ion. the energy consumed in branch 3 is a: times that consumed in branch --i when an elcctromotive forceacts in branch 1: therefore ial 'oi flsul 'i I 'Also the energy ,consun'icd in branch 1 is 1/ times that consumed in branchQ when an acts Ill branch 4'; whence I ($102111 y (S2162R1 Multiplying (1)) add (a) 1a) i a y( 2 -i F'I'()]1} nag :1. Obviously the expression given by formula (5 is a maximum when )::1. This means and (a?) it follows at once that .that for a given amount of telephonic energy developed in the transmitter at the transmitting substation a maximum amount is usefully delivered to the receiver at the receiving substation connected by the line, when 3,:1. Since the maximum amount of energy in the receiver is the prime desideratum of telephony. it would appear that the substation should be designed to make :1. Anotherconsideration.however.medifies this conclusion somewhat. namely, the effect of line noise. Since the line noise originates in the line the amount delivered to the receiver is proportional to (see equation 4.) while the amount of energy delivered from the transmitter of the communicating station is proportional to +1 1) (see equation 5). The ratio of the latter to the former is aiid this increases as 3/ increases beyond unitv. it will be clear. then. that if 3 is made greater than unity the substation (liscrimiuatcs against line noise as compared with the signals it is desired to receive. The amount of discrimination desired depends of course on the amount of line noise present. For conditions occurring in practice I have found by experiment that a desirable value for 1 is 1.4. \Yit'h this value of the over-all etlicienev is reduced to 2.8% below the maximum for I/:1. while the receiving ellicicncy alone is reduced 16.6%. it is thus-seen that a good degree of discrimination against line noise is obtained with a small loss in overall ctiicicnov.

The above consideratimis as to over-all etiiciene v and discrimination against line noise may be formulated as for an clectromotive force inserted in the line. In this equation is to have a value lying between 1 and 1.5 preferably.

Proceeding nowto a description of the circuit arrangeim nt ot' the substation shown in Fig. 2, L represents a telephone line terminating in ii substation arrangement comprising a transmitter '1. a receiver R. an auxiliary resistance X and a three winding induction coil, the designated N N and N The line I), winding! N receiver R and transmitter T are conncctedin a series circuit. \Vindings N and N are connected in series between the junction point a of the winding N, and the receiver R and the junction point (Z of the line, L and transmitter 'l. The auxiliary resistance X is connected between the juncwindings of which are tion oint e of the transmitter and receiver and t e junction oint b of the windings N,

and N,. A con enser may be inserted in S over the line.

The operation durin transmission is indicated m Fig. 3, in w ich the arrows represent the direc'tion of current flow at any. given'instant. When the transmitter T is operated, variations in the current flow are.

to apto t e produced, the eifect being equivalent plying a variable electromotlve force transmitter. At a given instant a current I equal to I flows from terminal d, throughthe transmitter T and auxiliary resistance 'X to terminal b. At terminal 6 the current divides and a current I, flows through windings N, and N over the line L to terminal (1, while the current l --I, flows in parallel therewith through' the winding N Potentials are induced in the windings of the transformer of such value and direction that terminals 0 and e are brought to the same potential, so that no current flows through the receiver during transmission and conse-- quently the substation is anti-sidetone.

The action during reception is indiiated in Fig. 4 and is as follows: Upon the application of a receiving potential to the inc terminals, a. current I, flows from terminal :1 over the line L and through the windin N to terminal a. A current I equal t6 flows from terminal a through the receiver R and transmitter- T to terminal :1. Since the current I is greater than the current I a current 1 -1, flows from terminal through the windings N and N, to termi'na Y c. Potentials are induced in the transformer windings of such value anddirection that terminals 6 and e are brought to the same potential, so that no current is wasted in the I auxiliary resistance during reception.

I The proportioning of the arran dment of Fig. 2 to satisfy the fundamenta requirements of the substation of my inventionwill now be iven. In deriving the design formulee, t e resistances of the t nsformer windings will be ignored.- It will e assumed further that there is no ma .et c leakage between the transformer win in'g and that the self impedances are very large compared with the impedances of any of the component elements of the substation or the impedance of the line; Experience has w n that these simplifying assumptions are ust1- fied and thatthe assumed conditions may be closelyrealized in practice by careful design.

To formulate the condition of con ugacy of the transmitter T and receiver R during transmisslon, assume an electromotive force 1n the transmltter clrcuit and assume that the required condition of conjugacy is satis fied. In other words assume that the terminals of the receiver are at points of equal potential with respect to an electromotive force applied to the transmitter. Let 1,, 1,,

I, and I denote the currents flowing in the transmitter, the receiver, auxiliary resistance and line, respectively, and R R R, and R, denotdthe resistances of the corre' sponding elements. The condition of conjugacy of the receiver with respect to the transmitter requires that no current flow through the receiver during transmission and hence 1 :0. It is also clear from Fig. 3 that I,==I Since the three windings of the transformer and the line are in a series circuit, the algebraic sum of the IR drop through the hue and the potential drops through the windings is zero, so that where K is the drop per turn of the trans former windings. Furthermore, since terminals c and e are at the same potential in Fig. 3, the algebraic sum of the IR drop through the auxiliary resistance and the drop through the winding N, is zero. Whence Kin -R 1 Also the algebraic sum of the ampere turns of the windings of the transformer must be zero, so that Referring now to Fig. at which shows the condition when receiving, it is apparent that I," equalsl Since terminals b and e are at the same potential, the algebraic sum of the IR drop through the receiver and the drop' through-winding N must be zero, so that we have I Similarly the algebraic sum of theIR drop through the transmitter and the potential Since the algebraic sum of the ampere turns of the transformer Wii we have dings must be zero,

- which maybe Written or, remembering that during reception 1 z @1 ffl2 4 i z s (10) Substituting the values given by equation (8) in equation (2) wehave Also since 1 :1 during reception, equation 6 may be written Collecting we have n a m m im i s) (W) =R4 Equating expressions (6) and (d) and designating the ratio 3 by 1-, we get i m I y Equation (6) may be Written Designating the ratios and as r and 1",

1 I i 3 I 3 this expression becomes (r+r+1) R I Collecting we transformer and all of these are ideal in :for an ideal' substation, v fore in this specification; stood therefore,

illustrated, but

viding-a substation ,comprising a single Substituting the value of 1" as given by equation 13 in the above expression, we have Substituting 7" and 1- have in equation (6;) we

Substituting the value of equation 13, this reduces to '1" as givenby for the substation shown in Fig. 2 the fol- It will be seen from the above formulae that the impedance of the receiver and auxiliary resistance are given in terms of the impedance of the transmitter and the ratio have as the design formulae y. It Will also be seen that the transformer ratios r and r are expressedin terms of the ratio 3 and the impedances of the trans- Consequently having lnitter and the line.

given the impedance ofthe li'ne' and transw mitter, upon selecting asuitable value for the ratio y, the remaining elements of the substation may lie-readily computed.

The type of substation disclosed above and I illustrated in the accompanying drawing is but one of a numbenemploying" only one and one auxiliary" resistance the sense that they satisfy the fundamentalrequirements It will be unnerthat "my invention Sis at! as stated liers-m limited to the specific embodiments liei-ein is broadly directed to protransformer and only one auxiliary element, which is so proportioned with reference to the line with which it is to be cotiperatively combined, that'it is ideally eilicient and substantially without side tone. Furthermore, I do not desire to limit the design of the substations herein disclosed and Illustrated to the accompanying design formulae. These formulae are derived on the assumption that ideal transformers are employed and that the component elements have no reactance, assumptions which are only approximately justified in practice. When particularly high precision is desired I may, therefore, proportion the substation more precisely by taking into account the fact that the transformer impedances are finite, and that the line and the various substation elements may have in general some reactance. The accompanying formulae however, give quite satisfactory results, and the methods by which the are derived will enable one skilled in t e art, to compute more precisely the substation constants when desired.

It will be understood that in the appended claims, where certain elements are said to be conjugate, or certain impedance relations are said to exist, since in practice these conditions can in general only be a proximated, these expressions will besatis ed by structures substantially conforming thereto, especiall' where some compromise with respect .to t e rigid requirements is necessary in order to discriminate against line noise. It will also be understood that while I have specifically illustrated and described m invention as embodiedil'i a telephone su station it is capable of many and varied embodiments which render it applicable in other kinds of signaling systems and consequently my invention is not to be limited to the particular form and use herein disclosed. It will be further understood that in this specification the word substation is employed in its generic sense and that consequently its significance is not limited to a subscrlbers telephone station but embraces broadly a telephone station including a repepter station for relaying telephonic signa s.

What is claimed is:

1. A signaling circuit comprising a transformer havin three windings, a ath for thetransmission and reception 0 signals, a path including transmitting apparatus, a path including receiving apparatus,- and a path including a balancing resistance, said first mentioned path and said three windings of the transformer being connected in a series circuit, said second and third mentioned paths being included in a series circuit bridged around two of said windings, and said fourth mentioned path bein connected between the junction point 0 said path including receiving apparatus,

two windings and the junction point of said second and third mentioned paths.

second and third mentioned paths, said ele mcnts being so proportioned and related that the impedance of the combination cornprising said transforz'ncr and said first, third and fourth mentioned paths, as seen from said second mentioned path, equal to the impedance of said second mentioned path.

3. A signaling circuit comprising a trans former having three windings, a path for the transmission and reception of signals, a path including transmitting apparatus, a path including receiving apparatus, and a path including a balancing resistance, said first mentioned path and said three windings of the transformer being connected in a series circuit, said second and third men tioned paths being included in a series circuit bridged around two of said windings, and said fourth mentioned path being connected between the junction point of said two windings and the junction point of said second and third mentioned paths, said ele ments being so proportioned and related that the im edance o the combination com prising sai induction coil and said second, third and fourth mentioned paths, as seen. from said first mentioned path, is equal to the impedance of said first mentioned path. 4. A signaling circuit comprising a trans former Having three windings, a path for thetransmisslon and reception of signals, a. path including transmitting zipparatus, a and a.

path including a balancing resistance, said first mentioned path and said three windings of the transformer being connected in a series circuit, said second and third mentioned paths being included in a series circuit bridged around two of said windings, and said fourth mentioned path being connected between .the junction point 0 said two windings and the junction point of said second and third mentionedpaths, said elements being so proportioned I and related that said third and second mentioned paths are conjugate. v

5. A signaling circuit COIIlpflSHlg a transformer having three windings,'a path for the transmission and reception of signals. a path including transmitting ap 'iaratus. a path including receiving apparatus, and a path including a balancing: resistance, said first mentioned path and said three windingsof the transformer being connected in a series circuit, said second and third mentioned paths being included in a series circuit bridged around two of said windings, and said fourth n'icntioned path bein connected between the junction point 0 said two windings and the junction-point of said second and third mentioned paths, said elements being so proportioned and related that said fourth and first mentioned paths are conjugate.

6. A signaling circuit comprising a'transformenhaving three windings, a path for the transmission and reception of signals. a path including transmitting apparatus. a path including receiving apparatus, and a path including a balancing resistance. said first mentioned path and said three windings of the transformer being connected in a series circuit, said second and third menthe impedance of the combination compris ing said induction coil and said second, third and fourth mentioned paths/as seen from said first mentioned path. is equal to the impedance of said tirst mentionedpath, said third and second.mentioned paths are conjugate and said fourth and first mentioned paths are conjugate.

In testimony whereof l have signed my name to this specification this 23d day of August. 1917.

WILLIAM H. MART] N.

Ill! 

